Liquid pumps have taken a variety of forms and have incorporated a variety of techniques for pressurizing liquid for transport. In those applications where very high pressures may be found useful, such as fuel injectors where the liquid is to be discharged into a combustion space, several unique difficulties present themselves. In such fuel injection environments, the liquid being transported by the injector is a hydrocarbon fuel.
One characteristic possessed by hydrocarbon fuels is that under the correct conditions of temperature, pressure, and air mixture the fuels will self-ignite. In diesel engines the fuel is ignited due to the high temperature of the compressed air in the vicinity of the injected fuel which causes the fuel, after a small time delay, to ignite in the hot air present. It is also possible to heat the fuel prior to injection into an air atmosphere to a temperature that will cause the fuel to spontaneously ignite, even if the air is not at an elevated temperature, that occurrence is often referred to as hypergolic ignition/combustion.
Fuel injectors have been investigated in which the fuel was heated remotely from the injector, and research has been done which characterizes the ignition properties of hypergolic combustion. One of the characteristics of the hypergolic fuel combustion process is that the onset of combustion begins after a shorter time delay following injection than occurs when fuel is injected into a hot compressed air space.
For good efficiency the spark ignited Otto engine requires the use of fuels having a high octane, that is a fuel which does not easily ignite when a mixture of fuel and air is compressed to a high temperature. Diesel engines on the other hand must be supplied with fuels of a high cetane number, that is fuels which will easily ignite when injected into the hot compressed air in the engine cylinder. Neither fuel works well in the other type of engine. The characteristic of a hot fuel injection is that fuels of either fuel quality of high octane or high cetane can be used without regard to the compression ratio or compression temperature existing within the engine cylinder. This property of the hot fuel (hypergolic) injector makes it possible for engines to operate on multiple fuels as mixtures or separately. The hot fuel injector can be used in engines currently described as Diesel, spark ignition Otto, Brayton (gas turbines), and Rankine cycle engines. In addition to potential use in the variety of internal combustion engines, the hot fuel injector can be used in furnaces, water heaters and other places where fuel combustion is desired.
Although the conditions required for injecting of heated fuels into internal combustion engines have been investigated by numerous researchers, none have been able to configure an injector which is suitable for production in commercial engine applications.